1. Field of the Invention
The present invention relates to an optical fiber composite power cable and more particularly to an optical fiber composite power -able having a loose-tube-type optical fiber impregnated therein which has improved tensile strength and which prevents the optical fiber from being compressed by metal conductors, even when excessive tensile force or bending force is applied to the cable, thereby remarkably reducing the generation of lateral pressure and thus optical loss.
2. Description of the Related Art
Recently, an optical communication method using an optical cable, namely a supreme transmission line for audio and data communication, has been increasingly developed. Thus, optical fiber composite power cables, provided with an optical cable and a power cable, which are impregnated therein, have become popular.
As shown in FIG. 2, an optical power composite interior cable supplied to customers, among the above optical fiber composite power cables, has a structure such that conductors 20 made of a copper wire and an optical fiber 13 are surrounded by a coating layer 40. A filling material 30 fills a gap between the conductors 20 and the optical fiber 13, and is contained in the coating layer 40.
In order to install the optical fiber composite power cable 1 at the end users' locations, such as offices, apartments, stores, etc., as shown in FIG. 1, the optical fiber composite power cable 1 is placed in an electric wire conduit 50 installed in a building. Here, excessive tensile force or bending force may be applied to the cable 1 placed in a part of the electric wire conduit 50.
In case that the excessive tensile force or bending force is applied to the cable 1, lateral pressure is imposed on the optical fiber 13 placed inside the cable 1, thereby causing optical loss. As shown in FIG. 2, since the optical fiber 13 together with the metal conductors 20 is surrounded by the coating layer 40, when tensile force or bending force is applied to the cable 1, the optical fiber 13 is compressed by the metal conductors 20, and the lateral pressure imposed on the optical fiber 13 becomes severe.
Since the optical fiber 13 of the conventional cable 1 is coated with a polymer 15, such as acryl, having a lower strength than that of the metal conductors 20, the optical fiber 13 is easily compressed by the metal conductors 20 when tensile force or bending force is applied to the cable 1, thereby increasing optical loss of the cable 1 due to the lateral pressure.
Recently, in order to reduce the lateral pressure of the cable 1, as shown in FIG. 3, a cable 1, of which reinforcement wires made 25 of metal are inserted into a central portion, has been developed.
Some parts of the cable 1, shown in FIG. 3, are substantially the same as those of the cable 1, shown in FIG. 2, and are thus denoted by the same reference numerals, even though they are depicted in different drawings, and a detailed description of the same parts will thus be omitted because it is considered to be unnecessary.
The cable 1 in FIG. 3 has a comparatively high reinforcing capacity against tensile force. However, since the reinforcement wires 25 compress the optical fiber 13 when tensile force or bending force is applied to the cable 1, they are not strong enough to prevent lateral pressure from being imposed on the optical fiber 13, thus being incapable of reducing optical loss of the cable 1.
Accordingly, in view of the recent trend toward the increasing use of cables, there is required a technique for removing lateral pressure imposed on the optical fiber.